Crystallization of mitochondrial cytochrome b-c₁ complex from gel with or without reduced pressure

Cytochrome b-c₁ complex (ubiquinol-cytochrome c reductase) of beef heart mitochondria has been crystallied. Crystals grown in capillary tubes diffracted X-rays from a laboratory source to a resolution of 7 Å and synchrotron radiation to a resolution of 4.5 Å in the presence of mother liquor. However, the movement of crystals in the mother makes data collection very difficult. Removal of the mother liquor from the crystals causes severe loss of diffraction quality. To circumvent these difficulties we have recently developed a metod for crystallization of the cytochrome b-c₁ complex from a gel. The sizes, shapes and diffraction qualities of crystals grown in gel approach those of crystals obtained from liquid. Preliminary experiments on a Xuong-Hamlin area detector indicate that these crystals have the symmetry of a body centered tetragonal space group with cell constants a = b 157 A ̊, c = 590 A ̊. Assuming eight cytochrome b-c₁ complex dimers per unit cell, the crystals have a solvent content of 70% (v/v). Under reduced pressure the crystallization time is significantly decreased. Although crystals obtained under pressure are generally smaller, the shorter crystallization time provides an opportunity to explore more crystallization conditions.